Twitter bug creates account hijacking peril

One-click vuln 'ridiculously easy to attack'

Twitter has been bitten by a hard-to-kill web-application bug that's being actively exploited to steal users' authentication credentials, a security expert said Tuesday.

A link that exploits the XSS, or cross-site scripting, vulnerability was included in tweets that sent users' session cookies to two servers under the control of attackers, according to Stefan Tanase, a security researcher for Russian anti-virus provider Kaspersky. The tweets, written in Brazilian Portuguese, claimed a popular band suffered a “tragic accident” and offered additional information.

The shortened link was clicked on more than 116,000 times, according to statistics from URL service bit.ly, although the actual number of people who fell for the attack is probably much smaller than that.

“We are currently working on taking down the malicious URLs and minimizing the damage as much as possible,” Tanase wrote. “Twitter along with other significant industry peers have of course been notified.”

He later updated the post to say that the vulnerability has been fixed.

Maybe, but at time of writing, Twitter was vulnerable to at least one other critical XSS hole that allowed attackers to steal authentication cookies with the simple click of a link. Mike Bailey, a web-application security expert with a firm called Mad Security, posted proof-of-concept code here. He told The Register the attack exploited a variation of the same bug Twitter supposedly fixed on Monday.

Sure enough, clicking the button caused our browser to tweet uncontrollably, but Bailey said the damage could have been much more extensive.

“I wrote this proof of concept in less than 10 minutes,” he wrote. “These things are ridiculously easy to attack. While this demo requires interaction, it doesn't have to. The entire attack could just as easily be completely silent.”

Bailey went on to say that his attack allows him to retrieve users' session cookies, which are sent once a correct password is entered.

To be sure, the attacks don't do much more than steal a cookie that allows an attacker access to a Twitter account for the remainder of the session, which is usually terminated when a user clicks the “sign out” link. Still, they're a reminder of the fragility of web security – and the uphill climb Twitter has if the site ever wants to become a trusted platform for its 105 million users. ®